Role of hypoxia-induced fibronectin-integrin β1 expression in embryonic stem cell proliferation and migration: Involvement of PI3K/Akt and FAK.

Cell migration is largely dependent on integrin (IN) binding to the extracellular matrix, and several signaling pathways involved in these processes have been shown to be modified by hypoxia. Therefore, the aim of this study was to determine the influence of hypoxia on fibronectin (FN) and IN β1 expression in mouse embryonic stem cells (mESCs) and their signaling pathways to modulate proliferation. FN and IN β1 expression were significantly increased in hypoxic mESCs by 24 h. Hypoxia also increased cell attachment, which was accompanied by concomitant increases in the binding level of FN and IN β1. Hypoxia-induced FN expression was mediated by increased phosphatidylinositol 3 kinase (PI3K)/Akt and mammalian target of rapamycin (mTOR) phosphorylation, and hypoxia-inducible factor-1α (HIF-1α) expression. Moreover, under hypoxic conditions, focal adhesion kinase (FAK) and Src phosphorylation were increased in a time-dependent fashion; these increases were blocked by IN β1 antibody. In addition, the hypoxia induced increase of F-actin distribution and cell migration (activation of matrix metalloproteinase-2 and -9) was inhibited by IN β1 antibody. Indeed, hypoxia increased the level of cell-cycle regulatory protein and DNA synthesis. In conclusion, hypoxia increases the proliferation and migration of mESCs via FN-IN β1 production through the PI3K/Akt, mTOR, and HIF-1α pathways, followed by FAK activation.